On 2013-09-30, Alexander Thesoso wrote:
I mean no disrespect to wood, people who work with it, or people who
measure it's moisture content.
I googled "wood moisture measurement".
As an outsider, I get the impression that measuring wood moisture
content is, as described, a crude, inexact process.
It is likely that, for most uses of wood, accurate and precise
measurements are not needed.
The reference process is: Weigh a piece of wood, dry it, weigh it
again. That is probably reasonably accurate and precise.
Probably -- if you can tell when the wood reaches a sufficiently dry
state to re-weigh it. :-) Perhaps bake it at a specified temperature
until another two hours does not produce more than a 1% change in the
weight.
The field process seems to be: Make an electrical resistance
measurement between a pair of pins driven an unspecified distance into
the wood, then look in a table to get and idea of the moisture for the
type of wood. Perhaps, use partly insulated pins to measure at some
(incompletely) specified depth.
There was one google hit for someone who simply drilled a couple of
spaced holes in a block, and drove a pair of nails through the holes
into the test piece, using the block as a depth stop. Then he simply
measured the resistance and looked up the moisture content.
As pure water is non-conductive, all the measurements seem to need
calibration for the salts/ion concentration of the specific wood.
Presumably, the sap constitution is sufficiently standard so it
produces the needed salts when in the just cut state. And thus the
drying would move the resistance along a known curve.
If I were still in the invention business, I'd develop and patent an
accurate, precise microwave wood moisture measurement device, but I no
longer care.
Nor is it clear that anyone needs the measurement to sufficient
precision to provide a market for such a device. :-)
So... The thing in the picture (2983) holds a couple of pins. The
robust device is bashed with a hammer to push the pins into a piece of
wood to an unspecified depth.
Since the exposed part of the pins has two diameters, I would
expect that you drive it in until the shoulder touches the surface of
the wood. (Given that said surface in the raw state is rather
inconsistent even if you strip off the bark first). :-)
If or when the pins bend or can't be
removed, they are replaced. There is probably some insulation on the
pin shanks so there is a reasonable chance of measuring the resistance,
then pulling the whole thing out and re-using it a few times. It now
all makes sense. I'm happy.
I'm not sure that there is insulation in the tool shown, nor on
the shanks of the pins -- but by loosening the screws in the sides, you
could withdraw the body and then measure the resistance between the pins
with no danger of the body shorting them. I think that the primary
function of the body is to be strong enough to drive them in without
problems, and built-in insulation appropriate to the apparent period of
the device may not survive that process with a serious hardwood. What
the tool *does* do is place the two pins at a precise spacing, and if
driven to the shoulders of the pins, at a repeatable depth, too.
Enjoy,
DoN.
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